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  • 1. Nuclear Chemistry Chapter 23
  • 2. Radioactivity
    • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934).
    • She discovered radioactivity , the spontaneous disintegration of some elements into smaller pieces.
  • 3. Nuclear Reactions vs. Normal Chemical Changes
    • Nuclear reactions involve the nucleus
    • The nucleus opens, and protons and neutrons are rearranged
    • The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy
    • “ Normal” Chemical Reactions involve electrons , not protons and neutrons
  • 4. Types of Radiation
    • Alpha ( ά ) – a positively charged (+2) helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons
    • Beta ( β ) – an electron
    • Gamma ( γ ) – pure energy; called a ray rather than a particle
  • 5. Other Nuclear Particles
    • Neutron
    • Positron – a positive electron
    • Proton – usually referred to as hydrogen-1
    • Any other elemental isotope
  • 6. Penetrating Ability
  • 7. Geiger-M ü ller Counter 23.7
  • 8. Geiger Counter
    • Used to detect radioactive substances
  • 9. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons A Z 1 1 1 0 0 -1 0 +1 4 2 23.1 X A Z Mass Number Atomic Number Element Symbol 1 p 1 1 H 1 or proton 1 n 0 neutron 0 e -1 0  -1 or electron 0 e +1 0  +1 or positron 4 He 2 4  2 or  particle
  • 10. Balancing Nuclear Equations
    • Conserve mass number (A).
    The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 235 + 1 = 138 + 96 + 2x1
    • Conserve atomic number (Z) or nuclear charge.
    The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 92 + 0 = 55 + 37 + 2x0 23.1 1 n 0 U 235 92 + Cs 138 55 Rb 96 37 1 n 0 + + 2 1 n 0 U 235 92 + Cs 138 55 Rb 96 37 1 n 0 + + 2
  • 11. 212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. 212 = 4 + A A = 208 84 = 2 + Z Z = 82 23.1 4 He 2 4  2 or alpha particle - 212 Po 4 He + A X 84 2 Z 212 Po 4 He + 208 Pb 84 2 82
  • 12. Nuclear Stability and Radioactive Decay Beta decay Decrease # of neutrons by 1 Increase # of protons by 1 Positron decay Increase # of neutrons by 1 Decrease # of protons by 1 23.2 14 C 14 N + 0  +  6 7 -1 40 K 40 Ca + 0  +  19 20 -1 1 n 1 p + 0  +  0 1 -1 11 C 11 B + 0  +  6 5 +1 38 K 38 Ar + 0  +  19 18 +1 1 p 1 n + 0  +  1 0 +1  and  have A = 0 and Z = 0
  • 13. Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1 Nuclear Stability and Radioactive Decay Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2 Spontaneous fission 23.2 37 Ar + 0 e 37 Cl +  18 17 -1 55 Fe + 0 e 55 Mn +  26 25 -1 1 p + 0 e 1 n +  1 0 -1 212 Po 4 He + 208 Pb 84 2 82 252 Cf 2 125 In + 2 1 n 98 49 0
  • 14. Learning Check
    • What radioactive isotope is produced in the following bombardment of boron?
    • 10 B + 4 He ? + 1 n
    • 5 2 0
  • 15. Learning Check
    • What radioactive isotope is produced in the following bombardment of boron?
    • 10 B + 4 He 13 N + 1 n
    • 5 2 7 0
  • 16. Write Nuclear Equations!
    • Write the nuclear equation for the beta emitter Co-60.
    60 Co 0 e + 60 Ni 27 -1 28
  • 17. Artificial Nuclear Reactions
    • New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4 He and 11 B.
    • Reactions using neutrons are called  reactions because a  ray is usually emitted.
    • Radioisotopes used in medicine are often made by  reactions.
  • 18. Artificial Nuclear Reactions
    • Example of a  reaction is production of radioactive 31 P for use in studies of P uptake in the body.
    • 31 15 P + 1 0 n ---> 32 15 P + 
  • 19. Transuranium Elements
    • Elements beyond 92 (transuranium) made starting with an  reaction
    • 238 92 U + 1 0 n ---> 239 92 U + 
    • 239 92 U ---> 239 93 Np + 0 -1 
    • 239 93 Np ---> 239 94 Pu + 0 -1 
  • 20. Nuclear Stability
    • Certain numbers of neutrons and protons are extra stable
      • n or p = 2, 8, 20, 50, 82 and 126
      • Like extra stable numbers of electrons in noble gases (e - = 2, 10, 18, 36, 54 and 86)
    • Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons
    • All isotopes of the elements with atomic numbers higher than 83 are radioactive
    • All isotopes of Tc and Pm are radioactive
    23.2
  • 21. Band of Stability and Radioactive Decay
  • 22. Half-Life
    • HALF-LIFE is the time that it takes for 1/2 a sample to decompose.
    • The rate of a nuclear transformation depends only on the “reactant” concentration.
  • 23. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?
  • 24. Kinetics of Radioactive Decay
    • For each duration (half-life), one half of the substance decomposes.
    • For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234
    After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams
  • 25. Kinetics of Radioactive Decay A = A 0 e ( -kt ) lnA = lnA 0 - k t A = the amount of atoms at time t A 0 = the amount of atoms at time t = 0 k is the decay constant (sometimes called  ) 23.3 t ½ 0.693 = k t ½ A daughter rate = -  A  t Ln 2 = k
  • 26. Radiocarbon Dating t ½ = 5730 years Uranium-238 Dating t ½ = 4.51 x 10 9 years 23.3 14 N + 1 n 14 C + 1 H 7 1 6 0 14 C 14 N + 0  +  6 7 -1 238 U 206 Pb + 8 4  + 6 0  92 -1 82 2
  • 27. Learning Check!
    • The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 31 hours?
  • 28. 23.8 Biological Effects of Radiation R adiation a bsorbed d ose ( rad ) 1 rad = 1 x 10 -5 J/g of material R oentgen e quivalent for m an ( rem ) 1 rem = 1 rad x Q Q uality Factor  -ray = 1  = 1  = 20
  • 29. Effects of Radiation
  • 30. Nuclear Fission
    • Fission is the splitting of atoms
    • These are usually very large, so that they are not as stable
    • Fission chain has three general steps:
    • 1. Initiation. Reaction of a single atom starts the chain (e.g., 235 U + neutron)
    • 2. Propagation . 236 U fission releases neutrons that initiate other fissions
    • 3. Termination .
  • 31. Nuclear Fission
  • 32. Nuclear Fission 23.5 Energy = [mass 235 U + mass n – (mass 90 Sr + mass 143 Xe + 3 x mass n )] x c 2 Energy = 3.3 x 10 -11 J per 235 U = 2.0 x 10 13 J per mole 235 U Combustion of 1 ton of coal = 5 x 10 7 J 235 U + 1 n 90 Sr + 143 Xe + 3 1 n + Energy 92 54 38 0 0
  • 33. Representation of a fission process.
  • 34. Mass Defect
    • Some of the mass can be converted into energy
    • Shown by a very famous equation!
    • E=mc 2
    Energy Mass Speed of light
  • 35. Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons. BE = 9 x (p mass) + 10 x (n mass) – 19 F mass E = mc 2 BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984 BE = 0.1587 amu 1 amu = 1.49 x 10 -10 J Converts amu to kg and multiplies by c 2 BE = 2.37 x 10 -11 J = 1.25 x 10 -12 J 23.2 BE + 19 F 9 1 p + 10 1 n 9 1 0 binding energy per nucleon = binding energy number of nucleons = 2.37 x 10 -11 J 19 nucleons
  • 36. Nuclear binding energy per nucleon vs Mass number 23.2 nuclear binding energy nucleon nuclear stability
  • 37. Nuclear Fission 23.5 Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions. The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass . Non-critical Critical
  • 38. Nuclear Fission & POWER
    • Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.
    • 17% of the world’s energy comes from nuclear.
  • 39. Diagram of a nuclear power plant
  • 40. Annual Waste Production 23.5 Nuclear Fission 35,000 tons SO 2 4.5 x 10 6 tons CO 2 1,000 MW coal-fired power plant 3.5 x 10 6 ft 3 ash 1,000 MW nuclear power plant 70 ft 3 vitrified waste
  • 41. Nuclear Fusion
    • Fusion
    • small nuclei combine
    • 2 H + 3 H 4 He + 1 n +
    • 1 1 2 0
    • Occurs in the sun and other stars
    Energy
  • 42. Nuclear Fusion
    • Fusion
    • Excessive heat can not be contained
    • Attempts at “cold” fusion have FAILED.
    • “ Hot” fusion is difficult to contain
  • 43. 23.7 Radioisotopes in Medicine
    • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure
    • 24 Na, t ½ = 14.8 hr,  emitter, blood-flow tracer
    • 131 I, t ½ = 14.8 hr,  emitter, thyroid gland activity
    • 123 I, t ½ = 13.3 hr,  ray emitter, brain imaging
    • 18 F, t ½ = 1.8 hr,   emitter, positron emission tomography
    • 99m Tc, t ½ = 6 hr,  ray emitter, imaging agent
    Brain images with 123 I-labeled compound
  • 44. Chemistry In Action: Food Irradiation Sterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning. 1000 to 10,000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit. 100 – 1000 kilorads Inhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables. Up to 100 kilorad Effect Dosage